High speed electronic r. f. vacuum switch



Sept. 20, 1960 R. H. GEIGER HIGH SPEED ELECTRONIC R.F. VACUUM SWITCHFiled March 25, 1958 INVENTOR :P/CHARD H 45/552 000 0 0. 4 0 0.0 n D P90w WO V D Q ATTORNEY atent Ofice 2,953,713 Patented Sept. 20, 1960 HIGHSPEED ELECTRONIC R.F. VACUUM SWITCH Richard H. Geiger, Emerson, N.J.,assignor to Roger White Electron Devices, Inc., Haskell, N.J., acorporation of New Jersey Filed Mar. 25, 1958, Ser. No. 723,752

3 Claims. ((1315-39) This invention relates in general to an electronicswitch and is more particularly directed to a transmission line typeelectronic vacuum switch operable at very high frequencies (VHF) andultra high frequencies (UHF).

The invention provides a method and apparatus by which rapid switchingrates are possible because of the inherent low inertia of the electronicmedium.

According to one embodiment of the present invention a coaxial type oftransmission line is provided having a gap in the inner conductor. Thegap in the line produces a discontinuity and therefore a change in thecharacteristic impedance normal to the line. This gap makes the lineimpedance appear capacitive for the particular frequency applicablethereto, the capacitive reactance be ing substantially greater than thelines characteristic impedance thereby giving the appearance of an opencircuit in the line. An electron cloud is introduced into the gap and isso adjusted that its plasma frequency (f is equal to or greater than thesignal frequency (f When these conditions have been satisfied the gapprovided in the line is effectively shorted to the applied frequency(fs)' may be changed provides a means of controlling the impedancecharacteristics of devices and apparatus having frequency sensitiveelements such as filters, tuned circuits and the like.

In another embodiment of the invention disclosed herein a magnetic fieldparallel to and surrounding the inner conductor of the coaxial line issuperimposed on the gap thus producing a cut-off of the anode current ina manner similar to the familiar cut-off of current in magnetrons. Thisform of operation reduces the power dissipation at the anode andproduces a greater electron density across the gap for the samepotential difference there-across.

, It is therefore an object of the invention to provide a high speedelectronic radio frequency vacuum switch sensitive to very highfrequency (VHF) and ultra high frequency (UHF) signals.

Another object of the invention is to provide a high speed electronicradio frequency variable impedance switching device for changing theimpedance characteristics of frequency sensitive apparatus.

Another object of the invention is to provide an electronic dischargeswitching device having reduced anode power dissipation and greatersensitivity to switching voltages.

Other objects and advantages will become readily apparent from a studyof the specifications and the accompanying drawings wherein:

Fig. 1 is a diagrammatic view showing a portion of a coaxialtransmission line partly cut-away with a gap in the line according tothe invention.

Figs. 2a and 2b are schematic diagrams of the coaxial transmission lineequivalent circuits in the open circuit state and closed circuit state.

Fig. 3 is a sectional view of a high speed electronic radio frequencyvacuum switch having a magnetic field The rapidity with which theimpedance of the line superimposed on the gap in the inner conductoraccording to another embodiment of the invention.

Now referring to the drawings and specifically with reference to Fig. 1there is shown an electronic radio frequency switch according to theinvention and generally designated by the reference numeral 10 andcomprising a coaxial transmission line 11 having an outer conductor 12and an inner conductor 13. The transmission line may be of the air typeor of the type having some dielectric medium interposed between theinner and outer conductors common to such type lines. The innerconductor 13 has a gap 14 introduced therein transverse to its axialdirection, and is a form of a re-entrant section of a coaxial line. Theinner line consequently is composed of two parts or elements 15 and 16spaced a distance apart which distance defines the gap 14.

Inner conductor element 16 has a recessed cylindrical portion 17extending from the gap inwardly some determinable distance and the innerconductor element 15 has centrally protruding therefrom a cylindricaloxide coated indirectly heated cathode 18 extending into and coaxialwith the recessed portion of element 16. Electrons emanating from thecathode 18 are produced by the application of some heater voltage. Thepotential difference between inner conductors 15 and 16, conductor 16being at a positive potential relative to inner condoctor 15, willproduce a current flow between the spaced inner conductors. The electrondensity created in the region defined by the separation of theconductors 15 and 16 is so adjusted as to satisfy the condition that theplasma frequency of the electron cloud, f in the gap region is equal toor greater than the signal frequency, 1, applied between the spacedinner conductors. When these conditions are fulfilled the gap 14 definedby the spaced inner conductor will be effectively shorted for theapplied signal frequency, f,,.

Figs. 2a and 2b show schematically how the control of the electrondensity in the air gap produces a transition from a line which lookscapacitive or open, Fig. 2a to a line which looks like it is terminatedin its characteristic impedance, Fig. 2b.

The inner conductors 15 and 16 and the cathode 18 therebetween are allcompletely enclosed by a glass envelope 19, the space enclosed by theenvelope being completely evacuated in the manner similar to vacuumtubes. Thus there is produced an electron discharge device which iscapable of rendering very rapid switching operations because of the lowinertia of the electronic medium.

Fig. 3 shows another embodiment of the invention wherein the gap definedby the spaced inner conductor elements is surrounded by a magnetic fieldextending in a direction parallel to the inner conductors and coaxialtherewith. The inner conductor generally designated by the referencenumber 21 comprises two separate portions 22 and 23 spaced at distancewhich defines an air gap 24 in a manner similar to that shown in Fig. 1.An indirectly heated cathode 25 extends from the inner conductor element22, at its central portion, inwardly towards the conductor element 23 atthe recessed part thereof also in the same manner as shown in Fig. 1.The cathode 25 is heated by filament wires 26 extending within the innerconductor 22 and the cathode 25. The anode portion 23 of the innerconductors has slotted portions 28 extending axially inwardly to lowerthe capacity of the gap and increase the open circuit impedance.

A magnetic field extending axially across the gap is produced by amagnet 29 coaxially surrounding the air gap and is so polarized as tocause the field to traverse a path from the cathode part of the innerconductor 22 to the anode portion 23 of the inner conductor. Themagnetic field across the gap enables a greater electron density toexist for the same voltage in the absence of such field, and alsoproduces cut-off of current flow from cathode to anode in' a mannercomparable to magnetrons thus reducing power dissipation at the anodeportion of the inner conductor. A glass envelope 30 surrounds the spacedinner conductors 22 and 23 and the gap defined thereby as Well as themagnet 29 associated with the gap. The space portion enclosed by theglass envelope is evacuated as previously explained with reference toFig. 1 so that an electron discharge device is produced having for itspurposes high speed switching at the upper frequencies of the energyspectrum such as at ultra high frequencies and at very high frequencies.

What is claimed is:

1. An electron discharge device operable as a fast acting transmissionline switch at high frequencies, said device comprising: a section of acoaxial transmission line having an inner and outer conductor, saidinner conductor including two spaced inner conductor elements, the spacebetween said two inner conductors defining a gap therebetween to causean open circuit in the line simulating high capacitive reactance;envelope means forming a substantially gas free enclosure surroundingthe gap between said inner conductor elements; electron emissive meanscoupled to one of said inner conductor elements; and means for creatingan electric field gradient between said inner conductor elements toextract electrons from said emissive means to produce an electron cloudbetween said elements at a fixed plasma frequency to cause the line toappear as a closed circuit terminated in its characteristic impedance atthe operating frequency, said plasma frequency and the frequency ofoperation being substantially equal.

2. An electron discharge device operable as a high frequencytransmission line switch said device comprising: a section of a coaxialtransmission line having an outer conductor, and an inner conductorhaving a gap therein to provide two spaced inner conductor elements, oneof said inner conductor elements having a cylindrical recessed portionextending inwardly from the gap, an indirectly heated cathode mounted onand extending from the other inner conductor element at the centralportion thereof into the recessed portion of said one inner conductorelement; means forming an evacuated envelope surrounding said gapbetween said inner conductor elements; and means for applying apotential across said inner conductor elements to produce a differenceof potential therebetween thereby producing an electron cloud betweenthe said conductors at a fixed plasma frequency to cause the line toappear as a closed circuit at the frequency of operation, said plasmaand operating frequency being substantially equal.

3. An electron discharge device operable at high frequencies for fastswitching comprising: a section of a coaxial transmission line includingan outer conductor, and two spaced inner conductor elements forming aninner conductor having a gap therein, one of said inner conductorelements being provided with slotted portions along the outer peripherythereof to lower the gap capacity and increase the open circuitimpedance of the gap whereby said gap normally appears as an opencircuit in the line; means for enclosing said gap in a relatively highvacuum; means disposed between the spaced inner conductor elements toproduce an electron cloud between said elements at a fixed plasmafrequency to cause the line to appear as a closed circuit at thefrequency of operation, said plasma and operating frequencies beingsubstantially equal; and magnetic means surrounding the gap to producean axial magnetic field across the gap from one of the inner conductorsto the other of the said inner conductors.

References Cited in the file of this patent UNITED STATES PATENTS2,557,961 Goldstein et al. June 26, 1951 2,643,297 Goldstein et al. June23, 1953 2,725,531 Fiske Nov. 29, 1955 2,795,760 Dench June 11, 19572,866,164 Steele Dec. 23, 1958

